A. Field of the Invention
The present invention relates generally to the medical diagnostic field and more particularly to a method and apparatus for detecting heart sounds and for generating accurately timed reference signals coincident with the first and second heart sounds of a cardiac cycle.
B. Description of the Prior Art
Various medical diagnostic methods and apparatus of the prior art have attempted to detect heart sounds and to distinguish between the first and second heart sounds by amplitude or by gating with the R wave of the ECG. Further, the prior art arrangements utilize the timing relationships between successive heart sounds and the first and second heart sounds for analysis purposes. Other prior art arrangements have attempted to synchronize, gate or trigger cardiac imaging apparatus on the basis of heart sound amplitudes, patient cardiac pulse signals, or electrocardiogram signals and delay techniques.
For example, U.S. Pat. No. 4,094,308 to Cormier detects heart sounds to develop an electrical phonocardiogram via an inverse filter network denoted as a deconvolution function. A phonocardiogram transducer is placed in contact with the chest of a patient whereupon acoustical energy of the heart sounds is converted into electrical energy. The resultant signal waveform after the deconvolution filter provides impulse functions for each heart sound with the basic purpose of the apparatus to determine the systolic time intervals such as: (1) the pre-ejection phase or period denoted as the elapsed time from the Q-wave onset (in the electrocardiogram waveform) to the opening of the aortic valve; or (2) the left ventricular ejection time equal to the length of time the aortic valve remains open as determined by the time difference between the two impulse signals. The apparatus distinguishes the impulses derived from the heart sounds on the basis of amplitude to establish timing markers for the measurement of the systolic time intervals and the accompanying heart rate. The larger amplitude signal is stated to occur during the closing of the aortic valve. Pulse height detection of the rectified signals resulting from the process is achieved with hysteretic comparators and with digital level converters regulating extracted voltages and current pulses to trigger digital logic networks and microcomputer circuits which selectively activate electronic counters, timers and dividers to measure the pre-ejection phase, the left ventricular ejection time, the ratio of these two quantities, and the heart rate.
U.S. Pat. No. 3,318,303 to Hammacher measures heart sounds by use of a contact microphone and provides outputs distinguishing the first and second heart sounds of each heart cycle by generating impulses coincident with each heart sound. While the first and second heart sounds are distinguished and separately analyzed, the first and second heart sounds are not differentiated by the timing relationships between the heart sounds in the overall heart cycle but merely by the state of a flip-flop which changes state upon the detection of each heart sound to thereby output two series of pulses, one for each heart sound in each heart cycle. The purpose of the Hammacher method and apparatus is to accurately determine heart beat frequency by comparing the periodic rates of each of the pulse trains corresponding to the first and second heart sounds and comparing the heartbeat frequency rate between the two pulse trains. Hammacher also mentions the detection of the first heartbeat by combination with the R-wave of the ECG.
U.S. Pat. No. 3,581,735 to Gentner, et al. is directed to phonocardiographic apparatus for measuring fetal heart frequency and utilizes the relationships of detected heart sounds in accordance with the overall period of the heart rate to detect missed heartbeats to provide accurate indications of the heart frequency. Specifically, the analysis utilizes physiological criteria to determine if heart sounds have been missed by comparing the time between successive detected heart sounds and the overall heart cycle to determine if an accurate heart frequency has been detected. For example, if the second heart sound is not detected and missed, a low heart rate frequency results and the ratio between successive heart sounds and the overall period is analyzed and if this ratio is approximately equal, it is determined that a heart sound has been missed; since at low heart rate frequencies such a ratio is physiologically impossible as the time between the first and second heart sounds is much less than the time between the second heart sound of the first cycle and the first heart sound of the next cycle for low frequency heart rates. However, if a high heart rate frequency is detected and the ratio is approximately equal, it is determined that an accurate heart rate frequency has been detected. There is no distinguishing between the first and second heart sounds as the systolic and diastolic events to differentiate the heart sounds.
U.S. Pat. No. 3,498,292 to Jorgensen, et al. is directed to a heart sound sequence indicator to detect and indicate the first and second heart sounds and their respective intervals on respective systolic and diastolic indicators. The determination and distinguishing of the heart sounds is achieved by derivation from the electrocardiogram waveform and appropriate timing circuitry and the arrangement does not directly detect or discriminate heart sounds.
U.S. Pat. Nos. 3,171,892, 3,954,098, 3,921,623, Re. 27,042, 3,878,832 and 3,132,208 are directed to various prior art techniques that analyze heart sounds for various purposes. For example, U.S. Pat. No. 3,171,892 utilizes an acoustic pickup device for detection of the fetal heart rate within another organism and utilizes pulse duration discriminator means to distinguish the fetal heart rate pulse waves from that of the mother by the pulse width of the heartbeat rate signals. U.S. Pat. No. 3,954,098 to Dick et al is directed to heart display apparatus and triggering of the display from a delayed ECG signal. U.S. Pat. No. 3,921,623 is directed to an acoustical heartbeat measuring circuit for analyzing specific frequencies occurring in the heartbeat and includes a filter having a predetermined frequency response to output an indication of a number of output signals. U.S. Pat. No. Re. 27,042 is directed to an examination of the characteristics of heart sounds as detected by a microphone pickup. An electrocardiogram sequencing network controls the systolic and diastolic interrogation intervals and thus the heart sounds are detected under control of the electrocardiogram sequencing. U.S. Pat. No. 3,878,832 is directed to a system for analyzing heart defects as detected by random noise from a composite signal that includes a periodic portion and a random noise portion. U.S. Pat. No. 3,132,208 is directed to a variable conductivity gate circuit for amplifier selectivity in an electronic stethoscope.
Considering various prior art techniques for utilizing heart sounds and/or ECG signals to control diagnostic display, U.S. Pat. No. 3,220,404 to DelLucchese is directed to a combined X-ray and phonocardiographic camera wherein the horizontal sweep of a display device is gated when heart sounds detected by a microphone exceed a predetermined level.
U.S. Pat. No. 2,190,389 to Strauss, et al. is directed to the control of X-ray apparatus by means of a heart movement or pulse beat pickup and providing an adjustable time delay to activate the X-ray tube of the apparatus. A pulse pickup is affected by means of a compression cuff or bag applied to the wrist with pressure variations being transmitted to act upon a piezoelectric crystal.
U.S. Pat. No. 3,825,751 to Geratsdorfer is directed to a method of activating X-ray apparatus by means of electrocardiogram signals and providing a predetermined delay to activate the apparatus for approximating the appropriate time of activation based on the electrocardiogram waveform.
U.S. Pat. No. 3,626,932 to Becker is directed to a method and apparatus for producing a double exposure, X-ray photograph of a heart at two different points during the cardiac cycle by causing an X-ray machine to produce an X-ray burst at a first given point in a cycle and then another burst at a second different point during the cycle. The method and apparatus utilizes a synchronizer for detecting the R-wave peak from electrocardiogram waveform and includes various adjustable pulse delay means for proper synchronization.
U.S. Pat. No. 3,557,371 to Becker is similarly directed to a method and apparatus for calibrating a cardiac X-ray synchronizer to cause an X-ray machine to produce an X-ray burst at a given adjustable point in the cardiac cycle of a patient disposed in the burst path. The R-wave peak in the electrocardiogram waveform is detected to produce a signal actuating the machine at a given adjustable time after the R-wave peak.
U.S. Pat. No. 2,152,045 to Gulland is directed to a body operated switch apparatus for synchronizing X-ray exposures utilizing a mercury switch mechanically operated by pulse, respiratory or other movements of the body and includes delayed action for timing exposures of X-rays or other photographs of the heart, lungs, etc.
U.S. Pat. No. 3,344,275 to Marchal, et al. is directed to radiology apparatus for effecting a simultaneous recording of a relatively slow variation of density such as of the lungs during respiration and also of the small variations of density due to the circulation of the blood. Activation of the two channels of information is controlled by an electrocardiogram input.
U.S. Pat. No. 4,240,440 to Groch et al. is directed to method and apparatus for obtaining a nuclear kymogram of regional heart wall motion in synchronism with a display of the ECG signal; the display being triggered under the control of the ECG signal.
Various other display arrangements controlled by the ECG signals are described in the following publications:
"Clinical Assessment of Left Ventricular Regional Contraction Pattern and Ejection Fraction by Height Resolution Gated Scintography", Berman et al., Journal of Nuclear Medicine, Volume 16, Number 10, pp. 865-874; PA0 "Thallium-201 Myocardial Imaging: Characterization of the ECG-Synchronized Imager", Hamilton et al., Journal of Nuclear Medicine, Volume 19, Number 10, pp. 1103-1110; PA0 "Left Ventricular Function in Acute Myocardial Infarction Evaluated by Gated Scintiphotograph", Rigo et al., Circulation, Volume 50, pp. 678-684, 1974; PA0 "A Real-Time System for Multi-Image Gated Cardiac Studies", Bacharach et al., Journal of Nuclear Medicine, Volume 18, Number 1, pp. 79-84, 1977; and PA0 "Comparison of Defect Detection or Ungated vs. Gated Thallium-201 Cardiac Imager", McKusick et al., Journal of Nuclear Medicine, Volume 19, Number 6, p. 725.
U.S. Pat. No. 3,993,995 to Kaplan, et al. is directed to a respiration monitor and utilizes arrangements for the automatic triggering of an X-ray machine at the instance of respiration extremes.
Thus, while the arrangements of the prior art have attempted to detect and distinguish between heart sounds, these prior art arrangements are not entirely suitable for accurately distinguishing between the first and second heart sounds and for providing accurately timed reference signals synchronized with the first and/or second heart sounds. Further, the prior art arrangements do not provide accurate and efficient diagnostic analysis to synchronize analysis data and/or images by accurately timed first and/or second heart sounds.